1. Field of the Invention
The present invention relates to a novel heterogeneous catalytic oxychlorination process for the preparation of chlorinated hydrocarbons, in particular for the production of 1,2-dichloroethane.
2. Description of the Prior Art
1,2-Dichloroethane (D 12) is a compound manufactured industrially on a scale of several million tons per year. Upon pyrolysis thereof, D 12 is converted into vinyl chloride monomer (VCM) and hydrochloric acid (HCl). The VCM is polymerized to poly(vinyl chloride) (or PVC) which is a widely used plastic material. The HCl produced in the pyrolysis is separated from the VCM and then contacted with ethylene and oxygen in the presence of a catalyst to prepare D 12; this constitutes the oxychlorination reaction.
The oxychlorination reaction is very general and can be carried out using most hydrocarbons. Catalytic oxychlorination has been described in numerous patents, in particular in FR 2,063,365, FR 2,260,551, FR 2,213,259 and FR 2,125,748. The catalyst is a copper salt deposited onto powdered alumina.
European Patent Application EP,58,644 describes the preparation of such a catalyst, by pouring a solution of cupric chloride into a fluidized bed of powdered alumina at a maximum temperature of 50.C. This operation is followed by fluid-bed drying in hot air at a temperature not exceeding 140.degree. C.
European Patent Application EP 29,143 describes the preparation of an oxychlorination catalyst, comprising mixing previously prepared catalyst, namely, alumina powder containing a copper compound, with a naked support, namely, alumina powder which does not contain any copper compound, in a fluidized bed during the oxychlorination reaction. The addition of a naked support to a fluid bed, originally charged with catalyst, during the oxychlorination reaction is also described.
This technique is stated to have the advantage of avoiding sticking (or agglomeration) of the catalyst grains during operation. The '143 application also describes a migration of the copper compound from the alumina containing the copper to the naked support. It is thus apparent that the result of this method is a reduction in the copper content of the catalyst, since the amount of support is increased without adding copper. Accordingly, the "suppression or reduction of sticking" is associated not only with the reduction in the amount of copper, but also with the migration of a copper compound from the alumina containing same to the naked support.
EP 29,143 also describes a technique for preparing a catalyst, in situ, by charging the reactor with naked support, fluidizing it with the reaction gas and adding solid cupric chloride thereto. This technique is presented as a substitute for the conventional preparation of the catalyst by impregnation external of the reactor. However, this preparation is suggested only on a laboratory scale, and such preparative technique indeed is not industrial, since, at the start of such preparation, the fluidized bed does not contain any actual catalyst, i.e., a copper compound deposited onto a support. Therefore, no oxychlorination reaction is carried out and it is necessary to initiate a heating stage. But if heating is carried out in the absence of catalyst, an explosive zone exists at the outlet of the fluid bed, because there is no reaction and therefore no conversion.
European Patent EP 119,933 also describes an oxychlorination catalyst based on the same principle as above, i.e., copper impregnating an alumina powder, but without presenting the disadvantage of agglomeration, because there is less copper on the surface than in the interior of the catalyst particles.
The above prior art all relates to fluid oxychlorination beds comprising a "homogeneous" catalyst, namely, all of the grains of which are impregnated with copper values.
Fluid oxychlorination beds including a "heterogeneous" catalyst, i.e., powders of a mixture of alumina particles impregnated with copper values as above and inert particles such as silica sand, have also been employed in this art. These catalysts are described in French Patent 2,242,143. Such "heterogeneous" catalysts do not present the disadvantage of agglomeration or sticking of the "homogeneous" catalysts but, on the other hand, they have the drawback of forming an auto-abrasive mixture, the grams of sand effecting wear and attrition of the alumina grains. The copper-rich fines are eliminated and this must be compensated for by additions of fresh catalyst.